CD4 and dry eye syndrome: In addition to the already discussed roles of Th1 and Th17 CD4+ T cells in dry eye and herpetic keratitis [8, 13, 14, 17, 73, 78], Th2 CD4+ T cells were shown to contribute to corneal epithelial barrier dysfunction in ocular allergy, a Th2-predominant immune disease in which corneal nerves are barely affected.